DEAPspace – Transient ad hoc networking of pervasive devices
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DEAPspace Transient ad hoc networking of pervasivedevices
Reto Hermann *, Dirk Husemann, Michael Moser, Michael Nidd,Christian Rohner, Andreas Schade
IBM Research Division, Zurich Research Laboratory, Saumerstrasse 4, CH-8803 Ruschlikon, Switzerland
The rapid spreading of mobile computerized devices marks the beginning of a new computing paradigm charac-
terized by ad hoc networking and spontaneous interaction, taking place transparently to the human user. The
DEAPspace project described in this paper aims at providing a framework for interconnecting pervasive devices over a
wireless medium. It supports the development of new proximity-based collective distributed applications. In this paper
we discuss the motivation of the project and describe possible new application scenarios from which requirements for
both the supporting framework and the underlying wireless medium are derived. Central research issues such as a new
push-model-based approach to fast and resource ecient service discovery, and encoding and match-making of
compact service descriptions, are elaborated in more detail. The paper also describes some related work and concludes
with a critical review of existing wireless communication technologies, followed by a description of the current state of
our project and an outlook on future research directions. 2001 Elsevier Science B.V. All rights reserved.
Keywords: Transient ad-hoc networking; Proximity based networking; Service advertising; Service discovery; Distributed service
discovery; Push model; Peer-to-peer communication; Service description; Multi-device applications; Bluetooth; IEEE 802.11; IEEE
802.15; HomeCast OpenProtocol
1. A world of connected devices
Most of the things we deal with in our day-to-day life are invisible from a computer science pointof view they either do not even contain a mi-croprocessor or they do not oer an interface tothe outside world, let alone communicate withother devices. Nevertheless, we already are sur-rounded by a host of devices containing a micro-processor of some sort. Moreover, we increasinglyencounter devices that not only contain an em-
bedded controller or system but in addition pro-vide an interface for exchanging data with otherdevices. It does not take a lot of imagination tocome to the conclusion that we are on the road toa world of devices that are not only controlled by amicroprocessor but also are capable of exchanginginformation with other devices through some kindof interface: already we carry with us GSM phones, personal
digital assistants (PDAs), digital watches, andother wearable devices;
very few oce environments survive without acomputer, printer, or network;
modern cars increasingly rely on computers notonly to control the operation of the car itself but
Computer Networks 35 (2001) 411428
* Corresponding author. Tel.: +41-1-724-8573.
E-mail address: firstname.lastname@example.org (R. Hermann).
1389-1286/01/$ - see front matter 2001 Elsevier Science B.V. All rights reserved.PII: S 1 3 8 9 - 1 2 8 6 ( 0 0 ) 0 0 1 8 4 - 5
also to provide additional services such as navi-gation, communication, and entertainment;
in our homes we use computerized devices tocontrol our home appliances, to entertain us,and to patrol our property;
and sensors that provide data about ourselvesand our environment pop up everywhere.Concurrently to the microprocessor pervasion,
wireless radio communication technologies (suchas Bluetooth or IEEE 802.11) become availablethat are first steps towards environments in whichcommunication is no longer wire-bound and eachdevice can cheaply communicate with other de-vices over some form of radio technology. Thecombination of information appliances with thesewireless networking technologies enables an entirerange of new applications and usage scenarios.
The DEAPspace project aims at providing aframework for interconnecting pervasive devicesover wireless communication technologies. Usingthis framework, devices that are in proximity toeach other can form ad hoc transient alliances tocreate new types of collective distributed applica-tions. To accomplish this goal, the followingquestions have to be answered. How can we findout about the information available and the ser-vices that devices oer? What kind of applicationsbecome possible? Can we provide a framework ofbuilding blocks for developing such applications?A particular focus of our work is on proximity-based networks and mobile nodes; in this context weneed to find out about available services in a fastmanner as communication relationships are po-tentially of rather short duration.
In the following sections we present a set ofapplication scenarios that capture the scope ofDEAPspace and, based on these scenarios, de-scribe the requirements, challenges, and goals ofour research and briefly discuss how our workcompares with existing, related research projects.The main part of our paper describes the under-lying service model and our approach to servicedescription, followed by a presentation and dis-cussion of the DEAPspace service announcementand discovery protocol. After a discussion of theexisting wireless communication technologies andtheir suitability for transient ad hoc networking,we conclude the paper by describing the current
state of our work as well as future research di-rections.
2. Application scenarios
As a basis for discussion we present three ap-plication scenarios. The first scenario illustrates amultidevice application where several devicesrender one virtual application. The second sce-nario is centered around a personal informationmanagement (PIM) application; here we useDEAPspace technology to hide data synchroni-zation. The third and last scenario illustrates acontext-aware application.
The first scenario describes a multidevice appli-cation. Alice wears a digital wristwatch, carries anultra-modern PDA containing not only the usualPDA applications (such as date book, addressbook), but also an attached MP3 player with aheadset including a microphone. In her backpackshe carries her GSM phone. With current tech-nology, when a phone call comes in, her GSMphone will start ringing, and all Alice can do iseither take down her backpack, open it, look forthe phone, check the phone to see who is calling,and decide whether to take the call, or she can justignore the call and hope that whoever is callingwill leave a message on the answering serviceprovided by her network operator.
With DEAPspace technology, her GSM phonediscovers her digital wristwatch and notices that itoers an alarm service, a limited display service,and an input service (the wristwatch has two but-tons). Instead of ringing in the backpack, the GSMphone invokes the alarm service of the digitalwristwatch, then the display service of the watch todisplay the number of the calling party, and theinput service of the watch to wait for Alice to ac-cept the call. Alice now merely has to glance at herwatch to find out who is calling and then press oneof the two buttons of the wristwatch to either ac-cept the call or ignore it. As the phone call is fromBob, her manager, she decides to accept the call.The GSM phone in the meantime has found outthat her MP3 player oers a voice output and in-put service; as soon as Alice has accepted thephone call through her wristwatch, the GSM
412 R. Hermann et al. / Computer Networks 35 (2001) 411428
phone connects with the MP3 player, and Alice istalking to Bob.
The second interesting scenario describes ahidden personal information management applica-tion. PIM refers to a set of applications such ase-mail, address book, calendar, to-do or task lists,shopping lists, user preference profiles, which aretypically jointly hosted on organizers, PDAs, lap-tops, and/or desktop computers. For the end-user,synchronization of the information across all de-vices becomes increasingly cumbersome and a taskin its own right. Wireless radio-based communi-cation technology can remedy the situation be-cause it can make the synchronization implicit,thus hiding it from the user. The followingscenario illustrates this transparency.
Bob has just left his home and is driving towork when his phone indicates with a beep thearrival of a message. His wife asks him to buysome flowers and bring them to dinner at hismother-in-laws place tonight. Whereas Bob mightwell forget the task after a days worth of work, herests assured that he will be reminded because hisphone has transferred the appointment message toboth his PDA and his wrist watch. In the oce heswitches on his desktop computer and startsworking through a full inbox of e-mails. Suddenly,a pop-up window alerts him that there is a con-flicting calendar entry. His secretary has scheduledthe video broadcast of the CEOs annual kickospeech and it happens to collide with his wifesrequest to shop the flowers. As Bob is well versedin the Weve had an outstanding year, but thisdoes not mean that . . . speeches, he decides toskip that speech and instead take care of theflowers as promised. Later that afternoon, while heis engaged in a lively discussion in one of his col-leagues oces, the alarm on his wrist sounds, re-minding him to leave for the flower shop.
The third scenario involves those situationswhere we could profit from context-related infor-mation and describes a context-aware application.Already today, information kiosks supply visitorsof exhibitions, museums, entertainment parks,malls, stations, airports, etc. with location-depen-dent information. Whereas now visitors must walkup to these kiosks to collect the information onpaper, radio-based communication technology al-
lows information kiosks to propagate informationto the persons information appliance. As the ki-osk detects the information appliance within radiorange, it tries to obtain user-specific context in-formation (age, gender, origin, etc.) and pushes thetailored information to the appliance. The arrivalinformation in the appliance may then issue analert to the user or, alternately, the informationmay simply be cached in the appliance with someadequate time-to-live. Let us look at an airportscenario in more detail.
Alice is driving to the airport to leave for abusiness trip when her car information systemalerts her of a trac jam on the route to airport.Unfortunately she cannot take another route and,thus, there is nothing she can do to avoid beingheld up. Alarmingly late she finally arrives at theairport car park, leaves her car and rushes to theelevator. While she is traveling to the departurefloor, the airport passenger information systemreads out the ticket details from her e-wallet.While still in the elevator, Alices attention isdrawn to her wristwatch by its alarm indicating thearrival of a message. As she hurries towards thedeparture hall, she reads on display of her watchthat she is to proceed directly to gate A37. Si-multaneously the security guards at the entrance toterminal A are alerted to her late arrival. As shewalks up to the checkpoint, they give her expeditedtreatment. Bypassing the queue, she passes thecheckpoint and proceeds to the gate where thehostess is already waiting for her. Minutes latershe is seated in the plane, breathless and thinkingthat perhaps taking the subway would not havebeen such a bad idea after all.
3. Requirements, challenges, and goals
Using these scenarios we can extract a set offeatures that define the scope of our DEAPspacework. A key feature is that applications can spanmultiple information appliances; that is, they aredistributed. Moreover, we target a wide range ofappliances: from small devices (such as a wrist-watch) to large devices (such as the elevator in theairport scenario); from devices designed to ac-complish a single function particularly well to
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devices that combine multiple functions in one box DEAPspace intends to be pervasive.
Another key feature illustrated in the previousexamples is hidden computing: the consumer isunaware of the applications executing. Applica-tions engage with one another triggered by certainevents such as the presence of a certain device in anenvironment. Applications may alert the user oncea result has been obtained, or cache the result forlater retrieval by the user. Related to hiddencomputing is another feature shared by our ex-ample applications, namely, spontaneous interac-tion. Interaction with a peer device is triggered bythe discovery of the device and its services. Next,appliances should be able to engage in applicationtransactions irrespective of whether they have metbefore; that is, we expect an ad hoc style of com-munication and application interaction. Tying inwith the ad hoc requirement is the desire to havetrue peer-to-peer communication without requiringa master to be present (nor should a master elec-tion process have to take place).
Then, proximity-bound computing and transientcommunication relationships are key features exem-plified by our scenarios. The limited radio range ofthe wireless communication technology employedby the appliances is used to establish spatial context(i.e., proximity). As we are dealing with mobileusers and mobile devices, communication relation-ships will be of short duration determined by therange of the wireless communication technologiesand the (relative) velocities with which devicesare moving through this range. Relative mobilityof devices can make this period arbitrarily small.
Also, applications will involve various mediatypes, possibly including audio, images and evenvideo data; thus, we need to be able to deal withmultimedia data.
As the transient communication relationshipfeature is frequently overlooked when evaluatingwireless communication technology let us illustratethis point in more detail. Assuming a mobile sce-nario with relative device velocity v and a wirelessrange r, the maximum time available for the ap-plication transactions to complete called interac-tion window tW, is given as tW 2r=v. Table 1illustrates the duration of the interaction windowsfor various mobility situations.
The execution of an application comprises anumber of activities, each adding to the total ex-ecution time tE required. These activities includediscovering a peer device or an existing network,creating or joining a network, discovering (all)peer application entities (i.e., service discovery),connection establishment (including parameternegotiation), transaction execution, and finallydisconnection.
Clearly, the following equation must hold:
tE < tW 2r=v:The primary goal of the DEAPspace research
project is the development of suitable algorithmsand formats (where necessary) and the imple-mentation of a ready-to-use framework for build-ing applications. Research issues that we haveidentified include prompt service discovery with-out a central service discovery server, compact andextensible service description, security in pervasivead hoc networks, configuration and managementof a lar...